Re: [PATCH] bdi: Move cgroup bdi_writeback to a dedicated low concurrency workqueue

Tejun Heo
2018-05-23T23:17:40Z

Hello, Rik.

On Wed, May 23, 2018 at 06:03:15PM -0400, Rik van Riel wrote:
> Dumb question. Does setting max_active to 1 mean
> that every cgwb_release_workfn() ends up forcing
> another RCU grace period on the whole system, while
> today you might have a bunch of them waiting on the
> same RCU grace period advance?
>
> Would it be faster to have some number (up to 16?)
> push RCU once, at the same time, instead of having
> each of them push RCU into a next grace period one
> after another?

Oh yeah, you're absolutely right. This would end up doing a lot of
back-to-back synchronize_rcu_expedited() calls which can't be good.
I'll send a patch to push it upto 16.

Thanks.

--
tejun